Conventionally, in RFID technology typically known for a contact-free IC card system, an antenna coil is built in an identification IC tag, such as an IC card, and forms inductive coupling with an electric wave released from a transmitter-receiver antenna of a reader/writer, such that data communication is performed.
Currently, a mode for performing data communication between an IC tag and a reader/writer is applied to, for example, making payments for train fares using an IC card. In such an example, when checking the usage of an IC card, a ticket-vending machine set in a train station or a specific viewer for reading data in the IC card is necessary. Moreover, in order to bill the IC card, the IC card must be billed (by cyber billing) on the Internet via, for example, a ticket-vending machine in a train station or a personal computer equipped with a reader/writer.
Such a mode for performing data communication between an IC tag and a reader/writer is expected to become more diversified in years to come. For example, in order to further increase the level of convenience, portable communication terminals, such as mobile phones and PDAs (personal digital assistants), will assumably be equipped with a tag function and a reader/writer function.
For example, by providing a mobile phone with a tag function, the mobile phone can be used to pay train fares by holding the phone up against the ticket gate. Furthermore, cyber billing can be achieved by using the communication function of the mobile phone. In addition, the outstanding balance in the tag included in the terminal can be checked by using the display function of the mobile phone.
Furthermore, by providing a mobile phone with a reader/writer function, the mobile phone can function alternatively as a ticket-vending machine in a train station. For example, this allows for checking of information related with the outstanding balance of other IC tags (IC cards), and also enables cyber billing.
As described above, if a mobile phone, for example, is equipped with both a tag function and a reader/writer function, a terminal body must carry designated antenna modules respectively for the tag function and the reader/writer function. In other words, when using the mobile phone as a tag, an antenna module used for communication with an external reader/writer is required. On the other hand, when using the mobile phone as a reader/writer, an antenna module used for communication with an external IC tag (IC card) is required.
Specifically, in recent RFID systems that operate at a frequency of 13.56 MHz, a proper operating environment is required. For example, with regard to communication properties, a longer communication distance is desired, or if the reader/writer and the IC tag are opposed to each other, a wide planar communication range is desired.
Generally, an important capability for an IC tag is communication distance, whereas an important capability for a reader/writer is communication range rather than communication distance. The communication property of an antenna module required for a tag function differs from the communication property of an antenna module required for a reader/writer function. Since these antenna modules require different antenna configurations, it is substantially impossible to satisfy the two functions with a single antenna coil.
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 8-194785) discloses a technology related with an improved reader/writer antenna coil for increasing the communication distance between an IC card and a reader/writer. Patent Document 2 (Japanese Unexamined Patent Application Publication No. 11-66260) discloses an IC card equipped with an antenna coil having an improved data transmitting efficiency. Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2002-15288) discloses a reader/writer that is capable of performing multi-communication with a plurality of different transponders (IC tags). Furthermore, Patent Document 4 (Japanese Unexamined Patent Application Publication No. 2002-325013) discloses an antenna module that prevents the communication properties from deteriorating, which may be caused by mutual interference with an attaching object.
On the other hand, in the field of electronic devices typically known for portable communication terminals, a lightweight, thin, compact structure is in great demand. This is achieved by, for example, size reduction, high-density packaging, and high integration of electronic components. Consequently, there is substantially no free space remaining for an addition of a new module for adding a new function. For this reason, incorporating the two above-mentioned types of antenna modules and a signal processing circuit thereof (RFID circuit) into the portable communication terminal automatically leads to a large dimension of the terminal body.
On the other hand, it is possible to inhibit the terminal body from becoming large in size by reducing the dimension of each antenna module. In that case, however, the communication properties are inevitably subject to deterioration. This is due to the fact that each antenna requires a certain surface area or more in order to satisfy the desired communication properties (communication distance, communication range, etc.).
In view of the circumstances described above, it is an object of the present invention to provide an antenna module that achieves a space-saving design as well as having both a capability for long communication distance for a tag function and a capability for wide communication range for a reader/writer function, and to provide a portable communication terminal equipped with such an antenna module.